Method of forming shallow trench isolation structure

ABSTRACT

A method of forming a shallow trench isolation (STI) structure in a substrate includes forming a pad oxide layer over the substrate. The method includes forming a nitride-containing layer over the pad oxide layer, wherein the nitride-containing layer has a first thickness. The method further includes forming the STI structure extending through the nitride-containing layer, into the substrate. The STI structure has a height above a top surface of the pad oxide layer. The method includes establishing a correlation between the first thickness, the height of the STI structure above the top surface of the pad oxide layer, and an offset between the first thickness and the height of the STI structure above the top surface of the pad oxide layer. The method includes calculating the height of the STI structure above the pad oxide layer based on the correlation, and selectively removing a determined thickness of the STI structure.

PRIORITY CLAIM

The present application is a divisional of U.S. application Ser. No.12/838,901, filed Jul. 19, 2010, which claims priority of U.S.Provisional Application No. 61/226,971, filed Jul. 20, 2009, which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The disclosure relates generally to integrated circuit manufacturingprocesses, and more particularly, to methods for controlling thedimension of a shallow trench isolation structure.

BACKGROUND

Shallow trench isolation (STI) has become a common and importantisolation technology in an IC device. One of the purposes of STI is toprevent carriers, such as electrons or electron-holes, from driftingbetween two adjacent device elements through a semiconductor substrateto cause a leakage current.

A conventional STI process flow may include pad oxide layer andnitride-containing layer deposition on a substrate, active area masking,nitride-containing/oxide etching, silicon substrate trench etching,isolation oxide filling, chemical mechanical polishing, andnitride-containing layer and pad oxide layer removal.

In the conventional method, the predetermined target height of isolationoxide above the pad oxide layer cannot be well controlled. In someproducts, the electrical performance varies with the predeterminedtarget height of isolation oxide. This lack of control also producesseveral problems, and one problem is divot formation (i.e. oxide recess)along an STI edge. Divot formation reduces device yield. The divot atthe edge of the STI may be formed by having the pad oxide layer removedin a wet dip process.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure will be described with reference to embodiments thereofas illustrated in the accompanying figures. It should be understood thatthe drawings are for illustrative purposes and therefore not drawn toscale.

FIG. 1 is a flowchart of a method for fabricating a shallow trenchisolation structure, in accordance with an embodiment of the presentinvention.

FIGS. 2 to 8 show cross-sectional views of a shallow trench isolationstructure at various stages of manufacture according to FIG. 1.

DETAILED DESCRIPTION

The making and using of illustrative embodiments are discussed in detailbelow. It should be appreciated, however, that the present inventionprovides many applicable inventive concepts that can be embodied in awide variety of specific contexts. The specific embodiments discussedare merely illustrative of specific ways to make and use the invention,and do not limit the scope of the invention.

FIG. 1 depicts a flowchart of a method 100 for fabricating a shallowtrench isolation structure according to one embodiment of the invention.FIGS. 2 to 8 are cross-sectional views of a shallow trench isolationstructure at various stages of manufacture according to FIG. 1.Referring to FIGS. 1 and 2, in process 101 step, a substrate 201comprises a pad oxide layer 203 formed on the substrate 201. The term“substrate” herein, generally refers to a semiconductor substratecomprising silicon or compound semiconductor, such as GaAs, InP, Si/Ge,or SiC. The pad oxide layer 203 has a top surface 202 and may be grownby a conventional oxidation process over the substrate 201.Alternatively, the pad oxide layer 203 may be formed by a chemical vapordeposition (CVD) process or any suitable method. In one embodiment, thepad oxide layer 203 has a thickness from about 90 Angstroms (Å) to about140 Å.

Referring to FIGS. 1 and 3, in process step 103, a nitride-containinglayer 205 is formed over the pad oxide layer 203 on the substrate 201.Examples of nitride-containing layer 205 may include a nitride layer, aSiON layer, or any suitable material. In one embodiment, thenitride-containing layer 205 has a thickness T from about 800 Å to about1600 Å. The nitride-containing layer 205 can function as a stop layerduring a subsequent process, such as for example planarization. In oneembodiment, the nitride-containing layer 205 has a top surface 206 andis formed by chemical vapor deposition (CVD). It is understood by thoseskilled in the art that nitride-containing layer 205 may be formed byother deposition process as well.

Referring to FIGS. 1 and 4-6, in process step 105, a shallow trenchisolation (STI) structure 211 is formed in the substrate 201. The STIstructure 211 extends through the nitride-containing layer 205, the padoxide layer 203 and into the substrate 201.

FIG. 4 illustrates a trench 207 that is etched and extends through thenitride-containing layer 205, the pad oxide layer 203 and into thesubstrate 201. The trench 207 may be formed by a plasma etching processor any suitable method.

FIG. 5 illustrates an isolation oxide layer 209 is deposited to overfillthe trench 207 and the top surface 206 of the nitride-containing layer205. In one embodiment, the isolation oxide layer 209 is a materialhaving a high gap fill characteristic, such as high-temperature undopedsilicate glass (USG), a high density plasma (HDP) oxide, or a siliconoxide such as tetraethyl orthosilicate (TEOS).

FIG. 6 illustrates the isolation oxide layer 209 being planarized toexpose the top surface 206 of the nitride-containing layer 205. Theplanarization process removes the portion of the isolation oxide layer209 that overfills the trench 207 to expose the top surface 206 of thenitride-containing layer 205. The planarization process may be performedusing a chemical mechanical polishing (CMP) process, an etching process,and/or a combination thereof. After the steps shown in FIGS. 4 to 6, theSTI structure 211 is formed and confined within the trench 207.

The STI structure 211 extends through the nitride-containing layer 205,the pad oxide layer 203 and into the substrate 201. The STI structure211 has a top surface 213 and a height H. The height H is measured fromthe top surface 202 of the pad oxide layer 203 to the top surface 213 ofthe STI structure 211. During the formation of STI structure 211, acorrelation between the thickness T of the nitride-containing layer 205and the height H of STI structure 211 is established in process step107. In one embodiment, the process 107 of establishing a correlationcomprises polishing the STI structure 211 to the nitride-containinglayer 205. The polishing makes the top surfaces 206, 213 of thenitride-containing layer 205 and the STI structure 211 substantiallycoplanar. Thus, the height H of STI structure 211 is substantially equalto the thickness T of the nitride-containing layer 205. In anotherembodiment, the process step 107 of establishing a correlation alsocomprises polishing the STI structure 211 to the nitride-containinglayer 205. But if CMP process has different removing rates for theisolation oxide layer 209 and the nitride-containing layer 205, there isa step height difference S between the top surfaces 206, 213 of thenitride-containing layer 205 and the STI structure 211. Therefore, ameasurement step may be needed to measure the step height difference S.

Referring back to FIG. 1, the fabricating method continues with process109. The thickness T of the nitride-containing layer 205 is measured tocalculate the height H of STI structure 211 according to the correlationin process step 107. The thickness T of the nitride-containing layer 205is measured by a metrology tool. The metrology tool may includeelectrical and optical tools, such as film thickness measurement tools,or any suitable tool. In one embodiment, if the top surfaces 206, 213 ofthe nitride-containing layer 205 and STI structure 211, respectively arealigned, the height H of STI structure 211 is substantially equal to thethickness T of the nitride-containing layer 205. In another embodimentshown in FIG. 6, if the top surfaces 206, 213 of the nitride-containinglayer 205 and STI structure 211, respectively are not aligned, themeasured height H of STI structure 211 is the measured thickness T ofthe nitride-containing layer 205 plus the step height difference Smeasured between the nitride-containing layer 205 and the STI structure211.

Referring again to FIG. 1, the fabricating method continues with processstep 111. The process step 111 determines a thickness D on the topportion STI structure 211 to be selectively removed in a first solution.As shown in FIG. 7, the thickness D of the top portion STI structure 211is a difference between the height H of STI structure 211 and apredetermined target height t′ of the STI structure 211 above the padoxide 203. An etching time for removing the thickness D could becalculated from the thickness D divided by a removing rate of STIstructure 211 in the first solution.

Referring back to FIG. 1, the fabricating method continues with processstep 113. The process step 113 selectively removes the thickness D ofthe top portion STI structure 211 by a first etching process. In oneembodiment, the substrate 201 is dipped in a first solution for theetching time calculated in process step 111. By controlling the etchingtime, the demand of a precisely controlled predetermined target heightt′ for STI structure 211 for different products can be achieved. In oneembodiment, the first wet solution comprises a HF solution, which isdiluted at a rate of 50:1. In another embodiment, the first wet solutioncomprises any suitable solution. In some embodiments, the process step113 comprises selectively etching the top portion STI structure 211 by adry etching process.

Referring to FIG. 1, the fabricating method continues with process step115. The process step 115 selectively removes the nitride-containinglayer 205 without etching the STI structure 211 or the pad oxide 203 bya second etching process. In one embodiment, the process step 115comprises dipping the substrate 201 in a second wet solution, whichcomprises a hot phosphoric acid solution. The second wet solution can bemonitored and controlled to keep the silicon concentration in the secondwet solution at a constant level, which is under an aggregate siliconconcentration. The silicon concentration directly affects the etch ratesof the nitride-containing and silicon oxide layers. For example, theoxide layer etch rate becomes dramatically lower as the siliconconcentration in the second wet solution increases. The siliconconcentration should be controlled under the aggregate siliconconcentration to prevent silica precipitates from forming in the secondwet solution. In one exemplary embodiment, the second wet solution maybe maintained at a predetermined temperature within a range of about 70to 160 to extend the bath life of the hot phosphoric bath. The siliconconcentration may be maintained at a predetermined concentration withina range of about 57 to 110 parts per million (ppm). In anotherembodiment, the predetermined temperature is at about 150° C. It isunderstood by those skilled in the art that the process step 115comprises removing the nitride-containing layer 205 by a dry etchingprocess as well.

It is understood by those skilled in the art that the predeterminedtarget height t′ may vary between different products. In some cases, theelectrical performance may vary with the predetermined target height t′of STI structure 211. The embodiments of the invention provide a methodto form a shallow trench isolation structure having a precisepredetermined target height control that achieves different demands fordifferent products with robust electrical performance.

FIG. 1 depicts a flowchart of the method 100 for fabricating a shallowtrench isolation structure for a single substrate. The method 100 canalso be simultaneously performed on all of the substrates in aprocessing lot. In another embodiment, all of the process steps exceptfor the measuring step 109 are simultaneously performed on all of thesubstrates in a processing lot, and the measuring step 109 is onlyperformed on a subset of the substrates in the processing lot. Forexample, all of the substrates in the lot can be processed togetherduring process steps 101, 103, 105 and 107. Since all of the substratesin the lot are processed together in those four steps, the correlationbetween the thickness of the nitride-containing and the height of theSTI should be similar for each substrate in the lot, so the measurementtaken on one substrate can be used to determine the thickness of STI tobe removed for all of the substrates in the lot. Thus it should not benecessary to measure the nitride-containing layer thickness on everywafer in the lot if all of the substrates in the lot are processedtogether during the other process steps. However, the measuring step 109may be performed on at least one substrate in the processing lot. Afterthe thickness of STI to be removed is determined in process step 111,all of the substrates in the lot can be processed together in processsteps 113 and 115.

One aspect of this description relates to a method of forming a shallowtrench isolation structure in a substrate. The method includes forming apad oxide layer over the substrate. The method further includes forminga nitride-containing layer over the pad oxide layer, wherein thenitride-containing layer has a first thickness. The method furtherincludes forming the shallow trench isolation (STI) structure extendingthrough the nitride-containing layer, the pad oxide layer and into thesubstrate, wherein the STI structure has a height above a top surface ofthe pad oxide layer. The method further includes establishing acorrelation between the first thickness, the height of the STI structureabove the top surface of the pad oxide layer, and an offset between thefirst thickness and the height of the STI structure above the topsurface of the pad oxide layer. The method further includes measuringthe first thickness of the nitride-containing layer. The method furtherincludes calculating the height of the STI structure above the pad oxidelayer based on the correlation. The method further includes determininga thickness of the STI structure to be removed according to a differencebetween the height of the STI above the pad oxide layer and apredetermined target height of the STI structure above the pad oxide.The method further includes selectively removing the determinedthickness of the STI structure. The method further includes selectivelyremoving the nitride-containing layer, after selectively removing thedetermined thickness of the STI structure, without substantially etchingthe STI structure or the pad oxide layer. The resulting STI structure ofeach of the first and second substrates has the predetermined targetheight above the pad oxide.

Another aspect of this description relates to a method of forming ashallow trench isolation structure in a substrate. The method includesforming a pad oxide layer over the substrate. The method furtherincludes forming a nitride-containing layer on the pad oxide layer,wherein the nitride-containing layer has a thickness. The method furtherincludes forming the shallow trench isolation (STI) structure extendingthrough the nitride-containing layer, the pad oxide layer and into thesubstrate. The method further includes planarizing the STI structure,wherein planarizing the STI structure generates an offset between a topsurface of the nitride-containing layer and a top surface of the STIstructure. The method further includes measuring the thickness of thenitride-containing layer. The method further includes determining aheight of the STI structure above the pad oxide, wherein the height ofthe STI structure above the pad oxide is determined based on acorrelation between the thickness of the nitride-containing layer, theoffset between the top surface of the nitride-containing layer and thetop surface of the STI structure, and the height of the STI structureabove the pad oxide. The method further includes calculating an etchingtime to selectively reduce a thickness of the STI structure in ahydrofluoric (HF) solution, wherein the thickness of the STI structureis a difference between the determined height of the STI structure and apredetermined target height of the STI structure above the pad oxide.The method further includes selectively reducing the thickness of theSTI structure in the HF solution for the etching time. The methodfurther includes thereafter selectively removing the nitride-containinglayer with a phosphoric acid solution without removing the STIstructure. The resulting STI structure has the predetermined targetheight above the pad oxide that remains on the substrate.

Still another aspect of this description relates to a method of forminga shallow trench isolation structure having a predetermined targetheight above a pad oxide layer on each substrate of a plurality ofsubstrates. The method includes forming a nitride-containing layer onthe pad oxide layer on each substrate of the plurality of substrates,wherein the nitride-containing layer has a thickness. The method furtherincludes forming the shallow trench isolation (STI) structure in eachsubstrate of the plurality of substrate to extend through thenitride-containing layer, the pad oxide layer and into a correspondingsubstrate. The method further includes measuring the thickness of thenitride-containing layer a single substrate of the plurality ofsubstrates to determine a height of the STI structure above the padoxide on the single substrate, wherein the height of the STI structureabove the pad oxide is determined based on a correlation between thethickness of the nitride-containing layer, an offset between a topsurface of the nitride-containing layer and the STI structure, and theheight of the STI structure above the pad oxide. The method furtherincludes calculating an etching time for each substrate of the pluralityof substrates based on the measured thickness of the nitride-containinglayer of the single substrate to selectively removing a thickness of theSTI structure on each substrate of the plurality of substrates in afirst wet solution, wherein the thickness of the STI structure is adifference between the determined height of the STI structure above thepad oxide layer and a predetermined target height of the STI structureabove the pad oxide. The method further includes dipping each substrateof the plurality of substrates in the first wet solution to selectivelyetch the thickness of the STI structure for each substrate for theetching time. The method further includes selectively removing thenitride-containing layer, after selectively etching the STI structure,for each substrate of the plurality of substrates without etching acorresponding STI structure or a corresponding pad oxide. The resultingSTI structure for each substrate of the plurality of substrate has thepredetermined target height above the pad oxide.

Although exemplary embodiments of the present invention and theiradvantages have been described in detail, it should be understood thatvarious changes, substitutions and alterations can be made hereinwithout departing from the spirit and scope of the invention as definedby the appended claims. Moreover, the scope of the present applicationis not intended to be limited to the particular embodiments of theprocess, machine, manufacture, and composition of matter, means, methodsand steps described in the specification. As one of ordinary skill inthe art will readily appreciate from the disclosure herein, processes,machines, manufacture, compositions of matter, means, methods, or steps,presently existing or later to be developed, that perform substantiallythe same function or achieve substantially the same result as thecorresponding embodiments described herein may be utilized according tothe present invention. Accordingly, the appended claims are intended toinclude within their scope such processes, machines, manufacture,compositions of matter, means, methods, or steps.

What is claimed is:
 1. A method of forming a shallow trench isolationstructure in a substrate, the method comprising: forming a pad oxidelayer over the substrate; forming a nitride-containing layer over thepad oxide layer, wherein the nitride-containing layer has a firstthickness; forming the shallow trench isolation (STI) structureextending through the nitride-containing layer, the pad oxide layer andinto the substrate, wherein the STI structure has a height above a topsurface of the pad oxide layer; establishing a correlation between thefirst thickness, the height of the STI structure above the top surfaceof the pad oxide layer, and an offset between the first thickness andthe height of the STI structure above the top surface of the pad oxidelayer; measuring the first thickness of the nitride-containing layer;measuring the offset; calculating the height of the STI structure abovethe pad oxide layer based on the correlation; determining a thickness ofthe STI structure to be removed according to a difference between theheight of the STI above the pad oxide layer and a predetermined targetheight of the STI structure above the pad oxide layer; selectivelyremoving the determined thickness of the STI structure; and selectivelyremoving the nitride-containing layer, after selectively removing thedetermined thickness of the STI structure, without substantially etchingthe STI structure or the pad oxide layer, whereby the resulting STIstructure of each of the first and second substrates has thepredetermined target height above the pad oxide layer, wherein theoffset between the first thickness and the height of the STI structureabove the top surface of the pad oxide layer is not equal to zero. 2.The method of claim 1, wherein said forming the STI structure comprises:etching a trench extending through the nitride-containing layer, the padoxide layer, and into the substrate; and depositing an isolation oxidelayer to overfill the trench.
 3. The method of claim 2, furthercomprising planarizing the isolation oxide layer, wherein theplanarizing generates the offset between the first thickness and theheight of the STI structure above the top surface of the pad oxidelayer.
 4. The method of claim 1, wherein selectively removing thenitride-containing layer comprises dipping the substrate in a phosphoricacid solution.
 5. The method of claim 4, further comprising: controllinga silicon concentration in the phosphoric acid solution within a rangeof about 57 to 110 parts per million (ppm).
 6. The method of claim 4,further comprising: controlling a silicon concentration in thephosphoric acid solution to be under an aggregate silicon concentration,whereby the STI structure is not removed.
 7. The method of claim 4,further comprising: during said dipping, maintaining the phosphoric acidsolution at a predetermined temperature.
 8. A method of forming ashallow trench isolation structure in a substrate, the methodcomprising: forming a pad oxide layer over the substrate; forming anitride-containing layer on the pad oxide layer, wherein thenitride-containing layer has a thickness; forming the shallow trenchisolation (STI) structure extending through the nitride-containinglayer, the pad oxide layer and into the substrate; planarizing the STIstructure, wherein planarizing the STI structure generates an offsetbetween a top surface of the nitride-containing layer and a top surfaceof the STI structure; measuring the thickness of the nitride-containinglayer; measuring the offset; determining a height of the STI structureabove the pad oxide layer, wherein the height of the STI structure abovethe pad oxide layer is determined based on a correlation between thethickness of the nitride-containing layer, the offset between the topsurface of the nitride-containing layer and the top surface of the STIstructure, and the height of the STI structure above the pad oxidelayer; calculating an etching time to selectively reduce a thickness ofthe STI structure in a hydrofluoric (HF) solution, wherein the thicknessof the STI structure is a difference between the determined height ofthe STI structure and a predetermined target height of the STI structureabove the pad oxide layer; selectively reducing the thickness of the STIstructure in the HF solution for the etching time; and thereafterselectively removing the nitride-containing layer with a phosphoric acidsolution without removing the STI structure, whereby the resulting STIstructure has the predetermined target height above the pad oxide layerthat remains on the substrate, wherein the offset is not equal to zero.9. The method of claim 8, wherein said forming the STI structurecomprises: etching a trench extending through the nitride-containinglayer, the pad oxide layer, and into each substrate of the plurality ofsubstrates; depositing an isolation oxide layer to overfill the trench.10. The method of claim 8, wherein said selectively removing thenitride-containing layer with the phosphoric acid solution comprises:controlling a silicon concentration in the phosphoric acid solution tobe under an aggregate silicon concentration, whereby the STI structureis not removed.
 11. The method of claim 8, wherein said selectivelyremoving the nitride-containing layer with the phosphoric acid solutioncomprises: controlling a silicon concentration in the phosphoric acidsolution within a range of about 57 to 110 parts per million (ppm). 12.The method of claim 8, wherein selectively removing thenitride-containing layer with the phosphoric acid solution comprisingmaintaining the phosphoric acid solution at a predetermined temperature.13. A method of forming a shallow trench isolation structure having apredetermined target height above a pad oxide layer on each substrate ofa plurality of substrates, the method comprising: forming anitride-containing layer on the pad oxide layer on each substrate of theplurality of substrates, wherein the nitride-containing layer has athickness; forming the shallow trench isolation (STI) structure in eachsubstrate of the plurality of substrate to extend through thenitride-containing layer, the pad oxide layer and into a correspondingsubstrate; measuring the thickness of the nitride-containing layer asingle substrate of the plurality of substrates to determine a height ofthe STI structure above the pad oxide layer on the single substrate,wherein the height of the STI structure above the pad oxide layer isdetermined based on a correlation between the thickness of thenitride-containing layer, an offset between a top surface of thenitride-containing layer and the STI structure, and the height of theSTI structure above the pad oxide layer; calculating an etching time foreach substrate of the plurality of substrates based on the measuredthickness of the nitride-containing layer of the single substrate toselectively removing a thickness of the STI structure on each substrateof the plurality of substrates in a first wet solution, wherein thethickness of the STI structure is a difference between the determinedheight of the STI structure above the pad oxide layer and apredetermined target height of the STI structure above the pad oxidelayer; dipping each substrate of the plurality of substrates in thefirst wet solution to selectively etch the thickness of the STIstructure for each substrate for the etching time; and selectivelyremoving the nitride-containing layer, after selectively etching the STIstructure, for each substrate of the plurality of substrates withoutetching a corresponding STI structure or a corresponding pad oxidelayer, whereby the resulting STI structure for each substrate of theplurality of substrate has the predetermined target height above the padoxide layer, wherein the offset is measured, and the offset between thetop surface of the nitride-containing layer and the STI structure is notequal to zero.
 14. The method of claim 13, wherein said forming the STIstructure comprises: etching a trench extending through thenitride-containing layer, the pad oxide layer, and into each substrateof the plurality of substrates; depositing an isolation oxide layer tooverfill the trench; and polishing the overfilled isolation oxide layerto expose the nitride-containing layer.
 15. The method of claim 13,wherein the second wet solution comprises a phosphoric acid solution.16. The method of claim 15, further comprising: controlling a siliconconcentration in the phosphoric acid solution to be under an aggregatesilicon concentration, whereby the STI structure is not removed.
 17. Themethod of claim 15, further comprising: maintaining a siliconconcentration in the phosphoric acid solution within a range of about 57to 110 parts per million (ppm).